WATER’S EFFECT
ON SHAPING
EARTH’S
SURFACE
10.4
OBJECTIVES
• Water is always on the move through the water cycle
• Explain that no matter what form water is in, it has the ability to reshape the surface of the
earth
• List the different ways water can reshape the surface of the earth
• Describe the two main processes in which water breaks down Earth’s landscape
• Describe what deposition is and how water builds up on features of the landscape
KEY TERMS
• Cave
• Delta
• Deposition
• Erosion
• Karst
• Landslide
• Rapids
• Striations
• Weathering (chemical, physical, biological)
INTRODUCTION
• It is hard to believe that snow falling down onto the surface of a rock can shape it.
• While one snowflake will not do this all by itself, many of them combined will over many
centuries
• If there is enough buildup of snow and ice and they begin to melt and slide down the surface of
a rock, they will scrape away, tear, crack, and carry away rock
• Imagine sandpaper over rock
INTRODUCTION
• While the formation of ice and snow as a glacier melting takes hundreds if not thousands of
years, there are faster ways to shape the landscape with water in its liquid form
• For example, a flash flood or landslide can immediately change the shape of the Earth’s surface
• Or another example over millions of years like the grand canyon
WEATHERING, EROSION, AND
DEPOSITION
• Water helps in the weathering, erosion and deposition processes
• Solid as a rock expression – always changing – wind, volcanoes, earthquakes, water
WEATHERING
• Weathering is the process in which
breaking down rock into smaller pieces
or fragments
• There are two types of weathering
– Physical weathering (aka mechanical) is
when rocks are broken down by force,
but still remain as the same kind of
rocks
• Chemical weathering where rocks are
broken down by chemicals into different
types of matter
Rope Swing Vid
WEATHERING PHYSICAL
• Physical weathering is when the rock is
scratched, scraped and broken into smaller
pieces and the composition or what is it made
up of does not change
• This is done by rocks being scraped by harder
rocks and breaking down
• Occurs most quickly where the climate
includes high levels of precipitation and large
temperature changes (between night and day,
and also from season to season)
• Ice wedging (aka frost wedging) weathers rocks
due to the expansion of water as it freezes
– Most common in BC
WEATHERING - CHEMICAL
• Chemical weathering is a chemical reaction that causes rocks to break down, or decompose.
• When a chemical reaction occurs, the minerals in the rocks change their composition and the
rock becomes weaker.
• Occurs most quickly where climate is warm, there is high levels of rainfall and pollution
• Water + oxygen = much chemical weathering, including rusting aka oxidation
WEATHERING - CHEMICAL
• Chemical weathering also occurs underground
• Carbon dioxide is the gas released by living things through respiration. When rainwater mixes
with CO2 in the atmosphere or carbon from organic materials on the ground, the water
droplets become acidic, meaning they form a mild acid called carbonic acid
• Carbonic acid + Calcium carbonate – baking soda and vinegar
WEATHERING - CHEMICAL
• Little by little as these small gaps are eaten away into rocks forming caves, sinkholes and karsts
• Much of our rock is made up of limestone which reacts well with the carbonic acid
WEATHERING – BIOLOGICAL
• Biological chemical weathering occurs if physical or chemical weathering has been caused by a
plant or animal
• the process is sometimes referred to as biological weathering
EROSION BY WATER
• Erosion by water
– Moving water breaks down rock
into sediment
• Sediment can be eroded far
away and deposited
– V-shaped valleys are carved by
flowing water
• Rapids create more weathering
as water moves faster
– Ocean waves continually erode
shoreline
– Gravity can cause landslides and
avalanches
EROSION BY ICE
• Erosion by ice
– Glaciers once covered all of BC (2 km deep, 10 000 years ago)
• leave striations (scratch marks) on rocks
• form U-shaped valleys
• can move large rocks long distances
EROSION BY ICE
• After erosion, sediments are eventually deposited
– A delta forms where a river empties into a calm basin
– Glaciers deposit many different forms of sediment
VIDEOS
• Grand Canyon
• Glaciers – Glace Ciiers
• Largest Ice Body